In wire matrix and other types of high-speed printing apparatus, such as that disclosed in U.S. Pat. 3,982,622, granted on Sep. 28, 1976, to J. A. Bellino, et al., the printing mechanism is positioned very close to the platen. An inked ribbon is positioned very close to the printing mechanism, between the printing mechanism and the platen. The paper which rests against the platen has very little clearance between the surface of the platen and the ribbon. This is an excellent arrangement for high speed matrix printing but leads to difficult paper insertion because of the very limited space between the ribbon and the platen.
Also, when the printing apparatus is mounted in a cabinet, the cabinet usually includes a paper-exit opening by which the printed paper can exit the cabinet. For aesthetic as well as practical reasons such as noise control, structural integrity, and operator safety, the paper-exit opening should be as small as possible. Such a desirably small opening exposes as little as possible of the interior machinery of the printing apparatus to the hazards of damage or the possibility of injury to an operator or others.
However, when the paper-exit opening is small, there is a great possibility that the leading edges of a sheet of paper, as it is inserted in the printing apparatus and advanced by rotation of the platen past the printing location and toward the paper-exit opening, will not always properly exit the machine cabinet but may jam by catching on the edge of the opening. This is particularly troublesome when the printing apparatus is operating unattended.
In conventional typewriters, as in the case of the IBM Executive, a sheet metal guide is arranged to hold the paper near the platen in an arcuate shape around the bottom of the platen. A second piece of sheet metal may actually bear against the platen and guide the paper very closely to the platen as the paper reaches the front of the platen, facing the keyboard. However, in the short length of the leading edge of the paper that extends from this final paper guide into the printing area, the paper is sufficiently rigid to extend tangentially from the platen. This cantilevered extension of the paper as the leading edge of the paper approaches the printing position is not a problem in a conventional typewriter with the ribbon and type bars placed a sufficient distance away from the platen and wherein the platen is very much exposed with the top of the paper eventually squeezed between the platen and a pair of upper guide rollers to keep the paper out of the way.
However, in the case of a printing apparatus in accordance with the abovementioned Bellino et al. patent, the printing apparatus with its platen and its facing inked ribbon is preferably enclosed within a cabinet. Therefore, the cantilevered, tangential extension of the paper is sufficient to catch and snag on the inked ribbon and perhaps jam on the edge of the paper-exit opening upon paper insertion. This is particularly a problem with multicarbon set-ups fed into the printer. Additionally, in the case of fan-fold paper in which the sections of the paper are connected by flexible paper hinges, these hinges tend to extend tangentially from the platen and may drag along the inked ribbon that extends across the width of the printing apparatus and these hinges may become unacceptably ink-smeared.